Both the diagnosis of breast cancer as well as the burden of breast cancer treatment put women at risk for emotional distress that may impair cancer-related immune function. The past decade has witnessed an increase in the number of women diagnosed with ductal carcinoma in situ (DCIS) due to the widespread use of screening mammography. DCIS is a growing clinical management challenge as there is limited knowledge of the natural history of DCIS. As a result women with DCIS face difficult treatment choices that must be weighed against not only the risk of cancer recurrence but also their personal values. Remarkably, there is little understanding of the psychological needs of women diagnosed with DCIS. Our preliminary data suggest that women with DCIS have elevated levels of mood disturbance, anxiety, and perceived stress, which are accompanied by immune dysregulation. The implication of such a psychological response upon cancer control mechanisms is considerable. Extensive evidence from the multidisciplinary field of psychoneuroimmunology (PNI) has demonstrated that emotional distress impairs immune function, including NK cell activity and cytokine balance. NK cells and cytokines participate in cancer control and contribute to the protection of an individual from tumor initiation, primary tumor growth, tumor metastasis, and also infectious disease. Therefore, the proposed study will use a PNI framework to investigate the dynamics of the psychological and immunological response of women newly diagnosed with DCIS. In addition, an evaluation will be made of the role of treatment decision-making on the psycho-endocrine-immune response of these women. The specific aims are to: 1) Evaluate the effect of increased mood disturbance, anxiety, and psychological stress on immune function in women who are diagnosed with DCIS (Stage 0) breast cancer at 4 time periods surrounding diagnosis and treatment. 2) Determine whether decisional conflict mediates the effects of mood disturbance, anxiety, and psychological stress on immune function in women who are diagnosed with DCIS. 3) Evaluate a mediation and moderation model of psychological stress and decision making in women diagnosed with DCIS by determining whether: (a) decision making characteristics (decision style, control preference, and satisfaction) moderate the level of decisional conflict experienced by women diagnosed with DCIS and (b) decisional conflict mediates mood disturbance, anxiety, and psychological stress reported by women diagnosed with DCIS. Women newly diagnosed with DCIS (N=122) will be enrolled. A prospective repeated measures design will be used to evaluate mood, state anxiety, psychological stress, serum cortisol, and immune function (NK cells and cytokines) of women with DCIS across the phases of diagnosis, treatment, and post-treatment follow-up. Results will be analyzed with respect to time and in comparison to a group of matched women without cancer. The knowledge obtained will advance the science of PNI by providing insight to the role of a cognitive factor (decision making) on the psycho-endocrine-immune response in women with DCIS. This insight may be used to guide the development of ways to manage decision conflict, which will reduce psychological distress and support immune function in women with breast cancer, as well as other populations facing high stakes treatment decisions.